1. Field of the Invention
The present invention relates to a plunging tripod-type constant velocity universal joint. In general, a constant velocity universal joint is one of universal joints capable of transmitting torque at constant velocity even when two shafts, namely, driving and driven shafts are joined together to form an angle. Of these joints, a plunging type allows a relative axial displacement between the two shafts by means of the plunging form of the joint, and a tripod type performs torque transmission with such a construction that a tripod member having three radially protruding trunnions is coupled to one of the shafts; a hollow cylindrical outer joint member having three axially extending track grooves is coupled to the other shaft; and the trunnions of the tripod member are accommodated in their corresponding track grooves of the outer joint member.
2. Description of the Related Art
One example of plunging tripod-type constant velocity universal joints will be described with reference to FIGS. 10A-10C. An outer joint member 1 has in its inner circumferential surface three axially extending cylindrical track grooves 2. A tripod member 4, inserted into the outer joint member 1, has three radially protruding trunnions 5 formed therein. On the cylindrical outer circumferential surface of each of the trunnions 5 is rotatably fitted an annular roller 7 via a plurality of needle rollers 6. The roller 7 is fitted in the track groove 2. A pair of roller guide surfaces 3 of each track groove 2 circumferentially opposed to each other are formed as concavely curved surfaces parallel to the axial direction, and the roller 7 of each of the three trunnions 5 has its outer circumferential surface formed as a convexly curved surface fitted in the roller guide surface 3. The rollers 7 are received in the roller guide surfaces 3 of their corresponding track grooves 2 so as to be movable along the track grooves 2 while rotating about the trunnions 5.
As shown in FIG. 10B, when torque is transmitted in a state where the joint takes an operating angle "THgr", the roller 7 and the roller guide surface 3 come into an obliquely intersecting relation to each other as shown in FIG. 10C. In this case, although the roller 7 tends to roll and move in a direction indicated by an arrow t in FIG. 10B, because the track groove 2 forms a part of the cylindrical surface parallel to the axis of the outer joint member, the roller 7 results in moving while being constrained by the track groove 2. As a result, slippage occurs between the roller guide surface 3 and the roller 7. This leads to occurrence of sliding resistance and further to occurrence of induced thrust in the axial direction. The sliding resistance and the induced thrust cause vibrations of a car body and noise, adversely affect the noise, vibration, or hardness (hereinafter xe2x80x9cNVHxe2x80x9d) performance of automobiles, and reduce flexibility in designing of car driving mechanisms, and thus should desirably be maintained.
As an example of plunging tripod-type constant velocity universal joints intended for reduction in such sliding resistance and induced thrust, there is known a construction shown in FIGS. 11A-11C. Specifically, as seen from the figure, a trunnion 5 of a tripod member 4 has a genuine spherical outer circumferential surface, and, on this genuine spherical outer circumferential surface is slidably fitted a cylindrical inner circumferential surface of a cylindrical ring 8. The ring 8 and a roller 7 constitute a roller assembly which is relatively rotatable via rolling elements. Needle rollers 6 are arranged between the cylindrical outer circumferential surface of the ring 8 and the cylindrical inner circumferential surface of the roller 7 as a so-called full complement of rollers, and are prevented from slipping off by an annular washer 9. The roller 7 is held inside a track groove 2 of an outer joint member 1 so as to be movable axially of the outer joint member 1 while rolling on a roller guide surface 3 of the track groove 2.
The trunnion 5 has its outer circumferential surface formed as a genuine spherical surface with its center of curvature located on the axis of the trunnion 5. The roller assembly (7 and 8) oscillates around the center of curvature. Since the roller assembly is free to oscillate, when torque is transmitted in a state where the outer joint member 1 and the tripod member 4 form an operating angle, the roller 7 is guided by the roller guide surface 3 of the outer joint member 1 so as to be kept parallel to the axis of the outer joint member 1, so that it correctly rolls on the roller guide surface 3 while being maintained in that position. This helps reduce sliding resistance occurring at the time when the joint operates at an operating angle and thus suppress the generation of sliding resistance and induced thrust.
As is conventionally known, a plunging tripod-type constant velocity universal joint is used to transmit torque from the engine system of an automobile to the wheels at constant velocity. The plunging tripod-type constant velocity universal joint has a spherical roller attached to the trunnion of the tripod member thereof. Between the outer circumferential surface of the trunnion and the inner circumferential surface of the spherical roller are arranged needle rollers acting as rolling elements as a full complement of rollers without a retainer. When torque is transmitted in a state where an operating angle is formed, induced thrust occurs during rotation due to mutual frictions occurring among the inner components. Further, even when the joint is deactivated, if the components are forced to be axially stretched, sliding resistance occurs. In regards to typical NVH phenomena encountered by automobiles, there are known, as one associated with induced thrust, transverse vibration of a car body occurring during running, and, as one associated with sliding resistance, an idling vibration phenomenon occurring when an automatic is at a stop with the range shifted to the drive or D-range.
NVH-related problems encountered by automobiles can be solved by reducing induced thrust and sliding resistance occurring in a joint in use. In general, since induced thrust and sliding resistance occurring in a joint tends to be dependent on the degree of the operating angle, the joint, when applied to a driving shaft of an automobile, needs to be designed under the constraint that the operating angle should be kept small. Thus, flexibility in designing car driving mechanisms of an automobile cannot be improved without reducing and stabilizing induced thrust and sliding resistance.
An object of the present invention is therefore to further reduce and stabilize such induced thrust and sliding resistance.
A constant velocity universal joint according to a first aspect of the present invention is provided with: an outer joint member having three track grooves formed therein, each of the track grooves having its roller guide surfaces arranged circumferentially opposed to each other; a tripod member having three radially protruding trunnions; a roller fitted in the track groove; and a ring fitted on each of the trunnions for rotatably supporting the roller so that the roller is movable axially of the outer joint member along the roller guide surface. In the constant velocity universal joint, the outer circumferential surface of the trunnion has a straight shape, as viewed in the longitudinal section, but has, as viewed in the cross section, a shape which allows contact with the inner circumferential surface of the ring in a direction orthogonal to the axis of the joint and allows creation of a gap between the outer circumferential surface and the inner circumferential surface of the ring in the axial direction of the joint, and wherein the ring has an inner circumferential surface shaped such that its diameter increases gradually from the axial central portion of the ring to the end-face side thereof.
Instead of being circular-shaped, as has been conventional, the outer circumferential surface of the trunnion is given a novel shape as described above. This allows, when the joint takes an operating angle, the trunnion to be inclined with respect to the outer joint member without changing the position of the roller assembly. Moreover, as is apparent from the contrast between FIG. 1C and FIG. 11C, a transversely elongated contact ellipse the outer circumferential surface of the trunnion forms with the ring is made approximate to a point. This helps reduce frictional moment acting to tilt the roller assembly. Therefore, the position of the roller assembly is stable at all times and thus the roller is maintained parallel to the roller guide surface, thereby achieving smooth rolling. Consequently, sliding resistance, as well as induced thrust, can be reduced.
Since the ring has an inner circumferential surface shaped such that its diameter increases gradually from the axial central portion to the end-face side, within a plane perpendicular to the joint axis, a comparatively large relative inclination is allowed between the trunnion and the ring. As a result, even where the roller assembly is forced to be slightly inclined with respect to the outer joint member, the smooth rotation of the roller assembly can be maintained without interference between the trunnion and the ring. Specific examples of such a ring as has an inner circumferential surface shaped such that its diameter increases gradually from the axial central portion to the end-face side includes: a ring having an inner circumferential surface in which the generatrix is composed of a part of an ellipse with its major axis extended in a direction orthogonal to the axis of the ring; and a ring having an inner circumferential surface in which the generatrix is composed of a combination of a circular arc with its radius of curvature made smaller in the central portion and a tangential line extending from both ends of the arc to the end face of the ring. In either case, since the width dimension of the ring is limited, the smaller the radius of curvature of the central portion of the generatrix, the larger the allowable relative inclination angle with respect to the trunnion can be secured. Here, it should be added that, the smaller the radius of curvature, the larger the contact surface pressure, and thus the range of the contact pressure needs to be defined from the strength and durability standpoints. In other words, it is preferable that the radius of curvature in question be made as small as possible so long as the contact surface pressure does not exceed the allowable upper limit.
The roller assembly is interposed between the trunnion and the outer joint member to serve to transmit torque. In a constant velocity universal joint of this type, since a direction in which torque is transmitted constantly coincides with a direction orthogonal to the axis of the joint, by bringing the trunnion into contact with the ring in the torque transmission direction, torque can be transmitted properly. Therefore, even though there exists a gap therebetween in the axial direction of the joint, it never occurs that the torque transmission is hindered.
Note that, although the ring and the roller constitute a roller assembly free to relatively rotate, they may make sliding contact with each other, or may have a plurality of rolling elements between them. Examples of the rolling element include a cylindrical roller, such as a needle roller, and a ball.
A constant velocity universal joint according to the second aspect of the present invention is characterized in that the generatrix of the inner circumferential surface of the ring forms a part of an ellipse with its major axis extended in a direction orthogonal to the axis of the ring.
A constant velocity universal joint according to the third aspect of the present invention is characterized in that the generatrix of the inner circumferential surface of the ring is composed of a combination of a central convex circular arc and a tangential line extending from the end portion of the convex circular arc to the end face of the ring.
A constant velocity universal joint according to the fourth aspect of the present invention is characterized in that when the joint is put under basic torque, a contact surface pressure between the trunnion and the ring is set to a range of 270 to 440 kgf/mm2.
A constant velocity universal joint according to the fifth aspect of the present invention is characterized in that when the joint is put under basic torque, the maximum contact surface pressure between the trunnion and the ring is set at 440 kgf/mm2, and that the radius of curvature of the inner circumferential surface of the ring is made as small as possible.
A constant velocity universal joint according to the sixth aspect of the present invention is characterized in that an allowable relative inclination angle between the trunnion and the ring in a loading direction is set to a range of 2 to 5xc2x0.
The present invention provides a constant velocity universal joint including: an outer joint member having three track grooves formed therein, the track groove having roller guide surfaces arranged circumferentially opposed to each other; a tripod member having three radially protruding trunnions; a roller fitted in the track groove; and a ring fitted on each of the trunnions for rotatably supporting the roller so that the roller is movable axially of the outer joint member along the roller guide surface. In this constant velocity universal joint, the outer circumferential surface of the trunnion has straight shape, as viewed in the longitudinal section, but has, as viewed in the cross section, a shape which allows contact with the inner circumferential surface of the ring in a direction orthogonal to the axis of the joint and allows creation of a gap between the outer circumferential surface and the inner circumferential surface of the ring in the axial direction of the joint, and wherein the ring has an inner circumferential surface shaped such that its diameter increases gradually from the axial central portion of the ring to the end-face side thereof. In this construction, when the joint takes an operating angle, the trunnion can be inclined with respect to the outer joint member without changing the position of the roller assembly. Moreover, the transversely elongated contact ellipse between the outer circumferential surface of the trunnion and the ring is made approximate to a point. This helps reduce frictional moment acting to tilt the roller assembly. Therefore, the position of the roller assembly is stable at all times and thus the roller is maintained parallel to the roller guide surface, thereby achieving smooth rolling. This contributes to reduction not only in sliding resistance but also in induced thrust.
Particularly, since the ring has an inner circumferential surface shaped such that its diameter increases gradually from the axial central portion to the end-face side, within a plane perpendicular to the joint axis, a comparatively large relative inclination is allowed between the trunnion and the ring. As a result, even where the roller assembly is forced to be slightly inclined with respect to the outer joint member, the smooth rotation of the roller assembly can be maintained without interference between the trunnion and the ring.
The constant velocity universal joint embodying the present invention is suitable particularly for an automobile""s drive shaft, because its use makes it possible to improve automobile""s NVH performance associated with the degree of sliding resistance and induced thrust, and to increase flexibility in designing car driving mechanisms.
The nature, principle, and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters.